To use the machine you need to capture a mob (Villager, Animal, Hostile Mob, etc) using a Safari Net. Once you have captured the mob in the Safari Net, place it in the Auto-spawner (in the only available slot).
When powered and supplied with Mob Essence the Auto-spawner will create the selected mob as long as it has met both the necessary essence and power requirements.
This video (below) demonstrates how to use the Auto-spawner in a self-sustaining, automatic mob farm supporting all mobs capturable by a Safari Net . The below video may not meet tutorial standards for demonstrative videos.